Battery pack enclosure with vent

ABSTRACT

Vented cells are held in a cell holder, which is also vented, to provide an escape path for gases that may be produced by failing or overloaded cells. The escape path leads to the outside of the cell holder, which is mounted in an enclosure forming the battery pack. The enclosure is also vented, via a pressure-relief valve, which allows for the escape of hot cell gases to the surrounding air. A cell holder is made up of a top tray, an intermediate tray and a frame. A venting path is formed between the top and intermediate trays.

TECHNICAL FIELD

This invention relates to a system for holding electrical cells. Morespecifically, it relates to a cell holder in a battery pack.

BACKGROUND

The demand for electrically based vehicles and devices has increasedthese last years due to their relatively low environmental impactcompared to prior technologies. The development of safer and moreefficient electrical cells and associated technologies is important forthe economic expansion of these fields.

Safely assembling and mechanically retaining battery cells in a batterypack can be difficult. Failure to correctly assemble the battery packsor loose cells in the packs may cause an electrical danger or fire,either during manufacturing, in use or in service. There are severalfailure modes that bring cells into a thermal runaway situation, whichmay impact neighboring cells and result in a battery pack igniting.

This background is not intended, nor should be construed, to constituteprior art against the present invention.

SUMMARY OF INVENTION

The present invention is a system for securing cells into a cell holder,which is vented. In some embodiments, an intermediate tray, a top tray,or both an intermediate and top tray define vents between top surfacesof the one or more cells and an exterior of the cell holder. The cellholder is mounted in a battery pack enclosure that is vented to thesurrounding air with a pressure relief valve, to allow gases fromfailing or over-used cells to escape from the battery pack. The gasesmay be hot, and may heat neighbouring cells, which may in turn overheat.By allowing the hot gases to escape, the risk of a thermal runaway isreduced.

Disclosed is a battery pack comprising: a plurality of cells, each cellhaving at least one vent; a cell holder in which the cells are held; atleast one vent in the cell holder that provides a venting path from thevents in the cells to outside of the cell holder; and an enclosurewithin which the cell holder is installed, the enclosure having apressure-relief valve; wherein the enclosure and the cell holder defineanother venting path, from the outside of the cell holder to thepressure-relief valve.

In some embodiments, the system may provide a small assembly strokedistance. The cells do not need to be pressed into place, which reduceschances of damaging a cell during the assembly of a cell holder. Thecell holder provides sufficient mechanical restraint of the cellswithout the use of traditional screws or connectors, which may otherwisebecome loose, creating the risk of electrical shock or fire.

The assembly of the cell holder involves slipping the cells into a framewith little to no force and then positioning an intermediate tray ontothe frame to help locate the cells. The cell holder is then secured witha top tray, which is a short stroke snap fit tray with integral locatingfeatures that locate it relative to the frame. The two parts of the trayassembly are snapped together to the frame in a pressing operation,securing the cells in place with no screws or fasteners.

Disclosed herein is a cell holder for one or more cells comprising: aframe that hosts one or more cells such that a portion of each cellprojects beyond a top of the frame; an intermediate tray on top of theframe and having one or more recesses each of which accommodate one ofthe projecting portions of the one or more cells; and a top tray on topof the intermediate tray and fastened to the frame through theintermediate tray, thereby holding the intermediate tray in place.

Also disclosed is a method for assembling a cell holder for one or morecells comprising: placing one or more cells in a frame that hosts theone or more cells such that a portion of each cell projects beyond a topof the frame; placing an intermediate tray over the frame, theintermediate tray having one or more recesses each of which accommodateone of the projecting portions of the one or more cells; connecting abusbar in the intermediate tray to a terminal on each of the one or morecells; placing a top tray over the intermediate tray; fastening the toptray to the frame through the intermediate tray, thereby holding theintermediate tray in place; and connecting another busbar in the toptray to a second terminal on each of the one or more cells.

BRIEF DESCRIPTION OF DRAWINGS

The following drawings illustrate embodiments of the invention, whichshould not be construed as restricting the scope of the invention in anyway.

FIG. 1 is a schematic drawing representing a sectional view of the cellholder seen from the side, according to an embodiment of the presentinvention.

FIG. 2 is a schematic drawing representing the cell holder seen fromabove, according to an embodiment of the present invention.

FIG. 3 is a schematic drawing representing a sectional view of the cellholder upper portion as seen from the side, according to an embodimentof the present invention.

FIG. 4 is a schematic drawing representing a sectional view of the cellholder bottom portion as seen from the side, according to an embodimentof the present invention.

FIG. 5 is a schematic drawing representing the cell holder seen from theside, according to an embodiment of the present invention.

FIG. 6 is a schematic drawing representing the cell frame seen fromabove, according to an embodiment of the present invention.

FIG. 7 is a perspective view of a cell holder, according to anotherembodiment of the present invention.

FIG. 8 is a flowchart describing the steps of the assembly process ofthe cell holder, according to an embodiment of the present invention.

FIG. 9 is a schematic cross-section of an upper portion of a cell holderwith vents, according to an embodiment of the present invention.

FIG. 10 is a schematic drawing of a battery pack enclosure, according toan embodiment of the present invention.

FIG. 11 is a schematic cross-sectional drawing of a portion of a batterypack enclosure, according to an embodiment of the present invention.

DESCRIPTION A. Glossary

Cell or electrical cell—this refers to a device capable of generatingelectricity from a chemical reaction. Cells may be rechargeable.

Clearance distance—this refers to the shortest distance through airbetween two conductors, such as the positive and negative terminals of acell. It may be a line of sight between the two conductors or it mayinclude multiple straight segments if there is an insulting obstructionon the direct path between the conductors.

Creepage distance—this refers to the shortest distance across thesurface of an insulator between two conductors, such as the positive andnegative terminals of a cell.

Busbar—this refers to a metallic strip, which is used as an electricalconductor for multiple components.

Snap lock—this refers to a device or a feature on a device that iscapable of fastening two or more components together. One component isfastened to another component by one portion of the snap lock being setin position relative to the other portion of the snap lock, either bysliding, rotating or any other suitable movement. Snap locks may bepermanent or temporary, or irreversible or reversible.

B. Exemplary Embodiments

Referring to FIG. 1 , there is shown a sectional drawing of the cellholder 2 as seen from the side. The cell holder 2 is an assembly of acell holding frame or cell frame 6, an intermediate tray 10 and a toptray 14. A cell 18 to be hosted by the cell holder 2 is inserted into acavity 20 present in the cell frame 6. A top portion of the cell 18projects upwards out of the frame 6. The intermediate tray 10 is placedon top of the cell frame 6 and has a recess 24 that accommodates theprojecting portion of the cell when the cell 18 is already in place. Theintermediate tray 10 and the cell frame 6 enclose the battery cells 18.

The top tray 14 is placed on top of the intermediate tray 10. The toptray 14 has studs 22 that are inserted into holes 26 of the intermediatetray 10 and then through to holes 30 in the cell frame 6. A positivebusbar 34 is located in the intermediate tray 10. A negative busbar 38is located in the top tray 14. The positive busbar 34 extends from theintermediate tray 10 into the hole 42 of the intermediate tray tocontact the positive terminal at the top of the cell 18.

The hole 26 in the intermediate tray 10 is aligned with the hole 30 inthe frame 6 in order for the stud 22 to slide properly through them. Thestud 22 has at its extremity a snap lock 46 that goes through theintermediate tray 10 to be fastened into the cell frame 6. The snap lock46 has a head that engages with a step 50 or other retaining surfaceformed between wider and narrower portions of the hole 30 in the cellframe 6. By locking the top tray 14 to the cell frame 6, the snap lock46 fastens the top tray 14, the intermediate tray 10 and the cell frame6 together. In some embodiments, the configuration of the snap lock 46of the stud is different. Any type of snap lock may be used so long asit fastens the top tray 14 to the cell frame 6 as the top tray and thecell frame are pressed together.

The deforming action of the snap lock 46 into the plastic mating feature50 in the cell frame 6 results in the cell 18 being retained in the cellholder as well as both the top tray 14 and the intermediate tray 10. Thesnap lock 46 slips easily into the cavities 26 and 30 in order to beengaged with the step 50 in the hole 30. The pressure needed to beapplied to the top tray 14 in order to fasten the assembly is generallylow. For example, the cell holder is fastened together using handpressure, which may be something more than that needed for a slip fitand something less than that needed for a press fit. The extent of themovement required to locate the top tray 14 ready for fastening is aboutequal to the height of the snap lock stud 26. The extent of the movementrequired to fasten the cell holder together is about equal to the heightof the snap lock 46. In other embodiments, the extent of the movementmay be reduced by making the height of the intermediate tray smaller,and by raising the locking feature 50 in the cell frame.

The trays 10 and 14 are made of a flexible material that provideselectrical insulation between the busbars 34 and 38. In otherembodiments, the material may be rigid. When fully assembled, the cellholder 2 may be considered to be touch-safe as the positive busbar islargely covered by the top tray 14 and the connection to the positivebusbar may be covered with a cap and/or located away from the exposed,negative busbar. Assembly workers, not being exposed to the cellterminals, can handle the assembled cell holder more safely. In someembodiments, a sealing material, adhesive or coating is placed betweenthe trays 10 and 14 and between the intermediate tray 10 and the cellframe 6. In some embodiments, a paper-like flame barrier material suchas Nomex® is incorporated into the cell holder 2 at positions where hotgas from the cells may come in contact with the plastic.

When the top tray 14 is locked into the cell frame 6, it isirreversible. This is achieved by using irreversible snap locks. In someembodiments, the assembly is reversible, using reversible snap locks,however in this case the strength of the assembly may be less than thatof an irreversible fit.

In some embodiments, the height of the assembly is checked after the toptray 14 is locked to the cell frame 6, via the intermediate tray 10, inorder to make sure that all the snap locks are engaged properly.

The cavity 20 in the cell frame 6 that hosts the cell battery 18 hasthree bottom protrusions 54 on its vertical wall. The bottom protrusions54 are spaced around the circumference of the cavity 20. In the samemanner, the recess 24 in the lower portion of the intermediate tray 10has three top protrusions 58. The top protrusions 58 and the bottomprotrusions 54 form guides to hold the cell 18 and secure it centrallyin position in the volume formed by the cavity 20 and recess 24. Eachset of protrusions 54, 58 aligns the cell in the center of the cavity 20or recess 24 in the respective plane of the protrusions.

The top protrusions 58 are molded on the wall of the recess 24 of theintermediate tray 10. The bottom protrusions 54 are molded on the wallof the cavity 20 of the cell frame 6. In some embodiments, the geometryof the protrusions 54, 58 in the cell frame 6 and intermediate tray 10is different to that shown in order for the intermediate tray and thecell frame to be more easily molded. In some embodiments, theprotrusions 54 and 58 are separate elements from the intermediate tray10 and the cell frame 6 rather than being integral with the trays. Thetop protrusions 58 and the bottom protrusions 54 prevent the cell 18from moving sideways or tilting in the cavity 20 and recess 24. As aresult, the top protrusions 58 and the bottom protrusions 54 facilitateefficient contact between the busbars 34 and 38 and the cells 18 duringassembly. The top protrusions 58 and the bottom protrusions 54 enforcean air gap around the cell 18. In some embodiments, the top protrusions58 and the bottom protrusions 54 have a rounded profile to avoiddamaging the wall of the cell 18.

At the bottom of the cavity 20 of the cell frame 6, there is a ledge 62.The ledge 62 supports the cell 18 from below. The ledge 62 and bottomsurface of the cell 18 form a well 66 to accommodate an epoxy resinmaterial that is used to adhere the cells to a cold plate. Heat from thecells is conducted away through the epoxy and the cold plate as currentis drawn from the cells, or as the cells are being charged. The bottomof the cell 18 is in contact with the epoxy resin material. In someembodiments, another material for thermal conductibility is used insteadof the epoxy.

Optionally, a locating feature 52 may be incorporated to locate theintermediate tray 10 in the correct location on the cell frame 6. Thelocating feature may be, for example, a boss projecting upward from theupper surface of the cell frame 10 and a corresponding recess in thebottom surface of the intermediate tray 10. One or more locatingfeatures may be incorporated into the cell holder. Other forms oflocating features may be used, such as a pin and hole combination, or aridge and slot.

In some embodiments, the cell frame 6, the intermediate tray 10 and thetop tray 14 are made of a plastic material, such as apolycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend polymer ora fiber reinforced polycarbonate. Different plastics may be used foreach of the cell frame 6, the intermediate tray 10 and the top tray 14.Different plastics may be used, for example, to tune a snap fit or toresist slumping when exposed to venting gases.

In some embodiments, for manufacturing purposes, the geometry of thecell frame 6 and the trays 10 and 14 may be different. For example, thewalls of cell frame 6 may be slightly inclined to facilitate the moldingprocess. Other lead-ins and molding drafts may also be incorporated.

In some embodiments, there are no protrusions 54, 58. Instead, therecess 24 in the lower portion of the intermediate tray 10 acts as aguide to align the cell 18 in the cavity 20 of the cell frame 6. To dothis, the recess 24 in the lower portion of the intermediate tray 10 issmaller in diameter than the cavity 20 that hosts the cell 18 in thecell frame 6. This way, the cell 18 positioned in the cavity 20 of thecell frame 6 is centered in the cavity 20 by the recess 24 of the lowerportion of the intermediate tray 10.

Referring to FIG. 2 there is shown the cell holder 2 as seen from above,with the top tray 14 and the negative busbar 38. The cell holder 2 hostsfive cells 18 with the negative terminal of each one of them connectedto ends 70 of the negative busbar 38.

Referring to FIG. 3 there is shown a top portion of the cell holder 2without the cell 18. The negative busbar 38 is inserted through a hole80 in the top tray 14 and a correspondingly aligned hole 82 in theintermediate tray 10. The holes 80, 82 are large enough to allow thenegative busbar 38 to be spot welded to the negative terminal, or crimp,of the cell 18. In some embodiments, the negative busbar 38 is bondedultrasonically to the cell terminals. The negative busbar 38 has anapproximately horizontal tab 84 that is flush with or enters slightlyinto the recess 24 of the intermediate tray 10, depending on theparticular dimensions of the cells 18 and the cell holder 2. Thenegative busbar 38 has a middle vertical section 88 and a top horizontalsection 92. The top horizontal section 92 fits into a slot in the topsurface of the top tray 14.

Referring to FIG. 4 there is shown a bottom portion of the cell holder2. The bottom protrusions 54 hold the cell 18 centrally in the cavity 20of the cell frame 6. The ledge 62 supports the cell 18. The ledge 62forms a well filled with epoxy resin material 100. The epoxy resinmaterial 100 glues the bottom of the cell 18 to a cold plate 102positioned underneath the cell frame 6. In some embodiments, there maybe a mechanical connection, using screws for example, of the cell holder2 to the cold plate 102 to ensure that there is an even pressure andflatness of the cold plate. The cold plate may be referred to as acooled plate, with cooling provided by circulating coolant fluid or byair cooling during operation. The use of screws here allows for thecompletion of the assembly of the cell holder before the glue cures.Such completion may involve, for example, the welding of the negativebusbar to the cells.

Referring to FIG. 5 there is shown the battery cell holder 2 as seenfrom the side. The top tray 10 is positioned over the intermediate tray14. The intermediate tray 14 is positioned over the cell frame 6.

Referring to FIG. 6 there is shown the cell frame 6 as seen from above.The cell frame 6 has cavities 20 with bottom protrusions 54 and ledges62. The cell frame 6 has cavities 30 that host the studs 22 from the toptray 14. In some embodiments, the ratio of snap locks to cells isbetween 1:1 and 10:1.

Referring to FIG. 7 there is shown an example of a cell holder 120 fornumerous cells. In some embodiments, a cell holder may be a module in abattery pack that has four or any other number of connected modules. Themodules are mechanically connected to each other, including theconnections between the busbars of the different modules. There is nowelding between adjacent modules. A module is thus the smallestchangeable unit of the battery pack if a defective cell needs to bereplaced.

C. Process

Referring to FIG. 8 , there is shown the steps to assemble the cellholder. In step 140, the cells are placed in the cell frame. Then instep 144, the intermediate tray is set over the cell frame with thecells already in place. After that, the positive busbar is connected tothe terminals in step 148, for example by welding. The top tray is setover the intermediate tray in step 152. Next, the top tray is fastenedto the cell frame in step 156, holding the intermediate tray in place.Optionally, the cold plate is then glued to the bottoms of the cells inthe cell holder, in step 158. After this, the negative busbar is weldedto the negative terminals in step 160.

D. Variations

Referring to FIG. 9 , an embodiment is shown in which there are ventpaths incorporated into the cell holder. The upper portion of the cell170 is shown with the intermediate tray 172 above and around it,locating it centrally in the recess of the intermediate tray with theprotrusions 174. The top tray 176 is located above the intermediate tray172, and has studs 178 that project down from the underside of theplanar portion of the top tray. Not shown are snap locks at the bottomof the studs 178 that hold the cell holder together. Positive busbar 180and negative busbar 182 connect to the terminals of the cell 170.

In contrast to other embodiments, this embodiment has vents 184, 186formed in the upper region of the intermediate tray 172. The vents 184,186 may be, for example, channels that are present in the upper surfaceof the intermediate tray 172. Other forms of the vents may be used inother embodiments. The vents 184, 186 allow hot gases from the cells 170to escape in the event that one or more of the cells begin to fail. Byallowing the hot gases to escape, the other cells around the failing onedo not get heated by the hot gases as much as if the gases did notescape.

Other implementations of the vent routing are possible in otherembodiments. For example, channels may be present in the lower surfaceof the top, planar portion of the top tray. The main requirement is toprovide a path that directs the hot gases away from the failing cell andto the exterior of the cell holder, so as not to cause a potentialthermal runaway effect.

Referring to FIG. 10 , multiple cells 200 are mounted in a cell holder202, which in turn is mounted in a vented battery pack enclosure 204.Vents 206 in the cells 200 are shown, as are vents 208 in the cellholder 202. Cells 200, which are vented, may be referred to as ventedcells. There may also be multiple cell holders in the battery pack. Thebattery pack enclosure 204, forming the exterior of the battery pack, isvented to the exterior environment via a pressure relief valve 210. Ifgases produced by the cells 200 reach a certain pressure, they canescape from the cells via the vents 206 in the cells, the vents 208 inthe cell holder 202 and the pressure relief valve 210.

Referring to FIG. 11 , the cell holder 202 and battery pack enclosure204 are shown, with the vents 208 in the cell holder. Spacers 220, 222maintain a gap 224 between the outer surface of the outer walls of thecell holder 202 and the inner surface of the inner walls of the batterypack enclosure 204. Gases produced by failing or overheated cells insidethe cell holder 202 escape in the direction of the arrows 226, 227, 228into the gap 224 between the cell holder and the battery pack enclosure204. A pressure relief valve 230 opens to release the gases that areproduced when they reach a certain pressure. The gases that are releasedescape in the direction of the arrows 231, 232 through the pressurerelief valve 230.

The cell holder may be made from electrically insulating plastics asdescribed above. The arrangement of vents in the cell holder may be asdescribed above, or may be located differently in other embodiments. Thetray system itself may be used to channel the gases that escape from thecell into a void between the different trays in the cell holderassembly. The trays in the cell holder may be made using aheat-resistant, fiber-reinforced plastic that can withstand elevatedtemperatures, such as temperatures up to 900° C., for example. Thepressure relief valve may be any suitable valve, which can withstand theexpected temperatures, such as a safety valve, a spring-loaded valve, abutterfly valve and an umbrella valve, for example.

In other embodiments, the snap lock engages with slots on the innersurface of the hole 30 rather than on a step. An alternate connectionmethod to join together the trays and the frame is a heat stake. Heatstaking has the advantage of the stake shrinking when cooled to tensionthe joint.

In other embodiments there are more than three protrusions 54, 58 ineach cell cavity. In other embodiments, there are two or even only oneprotrusion shaped like a rib that extends sufficiently around thecircumference of the cell cavity to centralize the cell. Busbars may beconnected to the polarities opposite to those described above.

In general, unless otherwise indicated, singular elements may be in theplural and vice versa with no loss of generality.

Depending on the embodiment, one or more of the advantages describedherein may be provided.

Throughout the description, specific details have been set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail and repetitions of steps and features have been omitted to avoidunnecessarily obscuring the invention. Accordingly, the specificationand drawings are to be regarded in an illustrative, rather than arestrictive, sense.

It will be clear to one having skill in the art that further variationsto the specific details disclosed herein can be made, resulting in otherembodiments that are within the scope of the invention disclosed. Allparameters, proportions, materials, and configurations described hereinare examples only and may be changed depending on the specificembodiment. Accordingly, the scope of the invention is to be construedin accordance with the substance defined by the following claims.

1. A battery pack comprising: a plurality of cells, each cell having atleast one vent; a cell holder in which the cells are held; at least onevent in the cell holder that provides a venting path from the vents inthe cells to outside of the cell holder; and an enclosure within whichthe cell holder is installed, the enclosure having a pressure-reliefvalve; wherein the enclosure and the cell holder define another ventingpath, from the outside of the cell holder to the pressure-relief valve.2. The battery pack of claim 1, wherein the cell holder is made withheat-resistant, fiber-reinforced plastic.
 3. The battery pack of claim1, wherein the cell holder is made usingpolycarbonate/acrylonitrile-butadiene-styrene.
 4. The battery pack ofclaim 1, wherein the cell holder comprises: a frame that hosts the cellssuch that a portion of each cell projects beyond a top of the frame; anintermediate tray on top of the frame and having recesses each of whichaccommodate one of said portions of the cells; and a top tray on top ofthe intermediate tray and fastened to the frame through the intermediatetray.
 5. The battery pack of claim 4, comprising, in each recess, one ormore protrusions on a wall of the recess to maintain the cell that isaccommodated by the recess centered in the recess.
 6. The battery packof claim 4, wherein the frame defines a cavity for each cell that ithosts.
 7. The battery pack of claim 6, wherein the recesses in theintermediate tray are aligned with the cavities in the frame.
 8. Thebattery pack of claim 7, wherein each recess has a smaller diameter thanthe corresponding cavity.
 9. The battery pack of claim 6, comprising, ineach cavity, one or more protrusions on a wall of the cavity to maintainthe cell that is in the cavity centered in the cavity.
 10. The batterypack of claim 6, wherein each cavity has a ledge at a bottom sectionthereof that supports the cell in the cavity.
 11. The battery pack ofclaim 10, wherein each cavity is open to a bottom of the frame.
 12. Thebattery pack of claim 11, comprising a cooled plate that is glued tobottom surfaces of the cells when the cells are in the cell holder. 13.The battery pack of claim 4, wherein: the top tray comprises studs eachwith a snap lock at its extremity; the intermediate tray defines holesthrough each of which one of the studs passes; and the frame definesfurther holes each with a retaining surface to which one of the snaplocks engage.
 14. The battery pack of claim 13, wherein each retainingsurface is a step in a wall of one of the further holes.
 15. The batterypack of claim 13, wherein a ratio of snap locks to cells is between 1:1and 10:1.
 16. The battery pack of claim 13, wherein the snap locks areirreversible.
 17. The battery pack of claim 13, wherein the snap locksare reversible.
 18. The battery pack of claim 4, comprising a negativebusbar in the top tray and a positive busbar in the intermediate tray.19. The battery pack of claim 4, comprising locating features in theframe and the intermediate tray that engage with each other.
 20. Thebattery pack of claim 4, wherein the intermediate tray, the top tray, orboth the intermediate and top trays define the venting path.